Composition for matte layer formation, release sheet using the same, and synthetic leather produced using said release sheet

ABSTRACT

There are provided a composition for matte layer formation suitable for the production of a matte synthetic leather having a matte surface with a high level of jet-blackness even without the practice of embossing, raising, etc., and a release sheet for the production of a matte synthetic leather by using the composition. The composition for matte layer formation suitable for the production of a matte synthetic leather comprises a thermosetting resin and a matting agent as indispensable components. The matting agent comprises one or at least two types of organic or/and inorganic porous fine particles. The porous fine particles have a mean particle diameter in the range of 0.5 to 20 μm and a specific surface area in the range of 1 to 1000 m 2 /g. The release sheet is produced by using the composition.

This is a Divisional of application Ser. No. 12/068,633 filed Feb. 8,2008, which in turn is a Division of Ser. No. 11/519,805 filed Sep. 13,2006, which in turn is a Division of application Ser. No. 10/328,188filed Dec. 26, 2002, now U.S. Pat. No. 7,169,457 issued Jan. 30, 2007.The entire disclosures of the prior applications are hereby incorporatedby reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a release sheet for the production of amatte synthetic leather and a composition for the formation of thesheet. More particularly, the present invention relates to a compositionfor matte layer formation suitable for the production of a mattesynthetic leather, which has a matte surface with a high level ofjet-blackness without the practice of embossing, raising or the like,and a release sheet for the production of a matte synthetic leatherusing the composition.

2. Prior Art

According to one of conventional production processes of syntheticleathers, a synthetic leather is produced by coating a composition for asynthetic leather, for example, a urethane resin, a vinyl chlorideresin, a polyamide resin, or an amino acid resin, on a release sheet,drying or curing the synthetic leather coating, coating an adhesive ontothe dried or cured coating, laminating a backing fabric, such as a wovenfabric, onto the adhesive coating, and then separating the release sheetfrom the synthetic leather composition coating. In this productionprocess of a synthetic leather, synthetic leathers having varioussurface shapes can be produced by regulating the surface form of therelease sheet. Specifically, since the surface shape of the syntheticleather is formed by transferring the surface form of the release sheetonto the synthetic leather, the regulation of the surface form of therelease sheet is necessary for the production of a desired syntheticleather.

One property required of synthetic leathers, particularly mattesynthetic leathers, is freedom from a faded color and is to bejet-black, that is, is to be matte.

For example, the following methods are known for the production of thesematte synthetic leathers. Specifically, in a conventional method, arelease sheet having concaves and convexes on its surface is produced,for example, by utilizing an emboss roll as a chill roll in the step ofextrusion lamination in the production of the release sheet or byutilizing an emboss roll as a chill roll in the step of forming anapplication film in the case of the formation of the release sheet bythe application of an existing film, and the concave/convex shape of thesurface of the release sheet is transferred onto a synthetic leather. Inanother conventional method, a release sheet with an emboss of concavesand convexes is prepared by embossing the whole release sheet, and theconcave/convex shape of the surface of the release sheet is transferredonto a synthetic leather. In a further conventional method, a syntheticleather having a matte surface is produced by subjecting a syntheticleather to raising.

The synthetic leathers produced by these methods are suitably matte.Since, however, the shape of fine concaves and convexes cannot beimparted by the embossing and the like, satisfactory jet-blacknesscannot be realized in synthetic leathers having a deep color, forexample, a black color. Further, in the methods wherein raising or thelike is carried out, a step should be additionally provided. Thisrenders the production process complicate and incurs increased cost.

On the other hand, as described in Japanese Patent Laid-Open No.158249/1985, a method for producing a matte synthetic leather, i.e., theso-called “synthetic leather with a matte tone,” has been developedwherein a composition for a release sheet with an inorganic pigment,such as silica or calcium carbonate, or a matting wax as a matting agentadded thereto is coated onto a substrate to form a release sheet.

In the release sheet formed by coating the composition with a mattingagent added thereto, however, the addition of a predetermined amount ofan inorganic pigment or the like to the composition is necessary forattaining satisfactory matte effect. However, when the amount of thisadditive added to the composition is excessively large, the so-called“drop of particles” wherein the matting agent is dropped from therelease sheet takes place.

Further, increasing the amount of the matting agent added for improvingthe matte effect causes aggregation of matting agent particles, and thematting agent disadvantageously bleeds out on the surface of the releasesheet. Therefore, a release sheet having desired fine concaves andconvexes cannot be formed, and, further, a synthetic leather, which ismatte and is jet-black, cannot be produced.

Further, in the composition, for a release sheet, containing fineparticles for matting purposes described in Japanese Patent Laid-OpenNo. 158249/1985 noted above, the incorporation of the fine particles canimpart a matte feel to some extent. However, it is difficult to providea synthetic leather which is jet-black without color fading.

The production of a matte synthetic leather by the conventional methodsinvolves, besides the above problems, an additional problem that theaddition of fine particles, which should be used as a matting agent forthe production of a matte synthetic leather, to the composition for arelease sheet deteriorates the fluidity of the composition and thusdeteriorates the coatability of the composition.

Further, coating of a coating liquid onto a substrate having lowsmoothness to form a release sheet poses problems of deteriorated dryingproperties and lowered smoothness of the release sheet due to drying bystrong heating.

When conventional paper is used as the substrate, static electricity islikely to be generated at the time of the formation of a release sheet.Further, in the production of a synthetic leather using this releasesheet, since the step of separating the synthetic leather from therelease sheet should be provided, the generation of static electricityis unavoidable. Thus, the generation of static electricity, for example,at the time of the production of a release sheet poses a problem ofcracking of the surface of the release sheet and the synthetic leather.

Accordingly, an object of the present invention is to provide acomposition for matte layer formation suitable for the production of amatte synthetic leather, which has a matte surface with a high level ofjet-blackness without the practice of embossing, raising or the like,and a release sheet for the production of a matte synthetic leatherusing the composition.

Another object of the present invention is to provide a release sheetfor the production of a matte synthetic leather, which release sheet hasexcellent smoothness and can realize the production of a good syntheticleather free from defects such as cracking by virtue of the suppressionof the generation of static electricity.

SUMMARY OF THE INVENTION

In order to attain the above objects of the present invention, accordingto one aspect of the present invention, there is provided a compositionfor matte layer formation, comprising a thermosetting resin and amatting agent as indispensable components, said matting agent comprisingone or at least two types of organic or/and inorganic porous fineparticles, said porous fine particles having a mean particle diameter inthe range of 0.5 to 20 μm and a specific surface area in the range of 1to 1,000 m²/g. The production of a release sheet by using thecomposition containing a matting agent comprising such fine particlescan realize the production of a synthetic leather with a matte tonewhich is jet-black without color fading.

In a preferred embodiment of the present invention, the porous fineparticles have been surface treated and have been homogeneouslydispersed in the composition for matte layer formation. More preferably,when the thermosetting resin is soluble in water, the surface treatmentis inorganic surface treatment, while, when the thermosetting resin isnonaqueous, the surface treatment is organic surface treatment. The useof the fine particles subjected to inorganic or organic surfacetreatment as the matting agent can improve the dispersibility of thefine particles in a coating liquid for matte layer formation. Therefore,even when the content of the fine particles in the coating liquid isincreased, the coatability of the coating liquid is not deteriorated.Further, since the fine particles are homogeneously dispersed in thecoating liquid, the coating liquid can form a matte layer having an evenconvex-concave surface.

Further, more preferably, the content of the porous fine particles inthe composition for matte layer formation is 5 to 50% by weight. Whenthe content of the fine particles is in the above-defined range, a mattesynthetic leather can be produced which is uniform and has a high levelof jet-blackness. Particularly preferably, the porous fine particles areselected from silica, calcium carbonate, talc, and a mixture containingat least one of said materials.

In a preferred embodiment, the composition for matte layer formationaccording to the present invention further contains a release agent. Theincorporation of the release agent in the composition for matte layerformation can lower peeling resistance at the time of the separation ofthe release sheet from the synthetic leather. Therefore, the releasesheet can be easily separated from the synthetic leather.

According to another aspect of the present invention, there is provideda first embodiment of the release sheet for the production of asynthetic leather according to the present invention, that is, a releasesheet for the production of a synthetic leather, comprising: a mattelayer formed by coating the above composition for matte layer formation;and a substrate for supporting the matte layer, said matte layer havinga fine concave-convex portion on its surface, said concave-convexportion having an arithmetical mean roughness (Ra) of 0.5 to 15 μm. Theuse of a release sheet having this surface shape can realize theproduction of a matte synthetic leather without the use of means such asembossing or raising.

According to still another aspect of the present invention, there isprovided a second embodiment of the release sheet for the production ofa synthetic leather according to the present invention, that is, arelease sheet for the production of a synthetic leather, comprising: amatte layer having fine concaves and convexes on its surface; and asubstrate for supporting the matte layer, said matte layer comprising areleasable resin layer, a releasable transparent resin being provided soas to stay on the bottom of the concaves in the concave-convex portion.The production of a synthetic leather using this release sheet can morereliably impart peach skin-like appearance and feel to the surface ofthe synthetic leather. Further, even in the repetition of the productionof synthetic leathers with different colors, since the releasabletransparent synthetic resin stays on the bottom of the concaves in thefine concaves and convexes, the release sheet has excellentreleasability. Therefore, the release sheet can be repeatedly used.

Further, in a preferred embodiment, the concave-convex portion has anarithmetical mean roughness (Ra) of 0.5 to 15 μm, the mean spacing ofprofile irregularities (concaves and convexes) (Sm) in theconcave-convex portion is 0.5 to 10 μm, and the mean inclination (θa) ofsaid concaves and convexes is 45 degrees≦θa<90 degrees. The matte layerhaving this concave-convex surface can be formed by coating the abovecomposition for matte layer formation.

In the above first and second embodiments of the release sheet for theproduction of a synthetic leather, a smoothing layer is preferablyprovided between the matte layer and the substrate. The provision of thesmoothing layer on the substrate can realize the production of a releasesheet having a uniform fine concave-convex surface without the influenceof the surface of the substrate.

More preferably, the smoothing layer has been formed using a compositionhaving the same formulation as the above composition for matte layerformation except that the porous fine particles are absent in thecomposition. The use of this composition as the composition forsmoothing layer formation can form a smoothing layer which has increasedadhesion to the matte layer and thus can prevent interlaminar peeling.In particular, the incorporation of a leveling agent in the smoothinglayer can further improve the smoothness.

According to a further aspect of the present invention, there isprovided a third embodiment of the release sheet for the production of asynthetic leather according to the present invention, that is, a releasesheet for the production of a synthetic leather, said release sheetcomprising: a matte layer formed by coating the above composition formatte layer formation; and a substrate for supporting the matte layer,wherein said matte layer is a releasable resin layer having a multilayerstructure of at least two layers, all the releasable resin layersconstituting the multilayered matte layer except for at least the layerin contact with the surface of the substrate contain a release agentcomprising a silicone-modified resin or a silicone-containing resincomposition, and the content of the release agent is larger as thereleasable resin layer is closer to the surface of the matte layer. Theadoption of a multilayer structure of two or more layers in thereleasable resin layer is advantageous in that, even when the thicknessof the releasable resin layer should be increased due to low smoothnessof the substrate, the thickness of each layer can be reduced and, at thesame time, the layer near the substrate side can further improve thesmoothness. Therefore, a lot of time is not required for drying thecoating liquid. Further, in the layers other than the layer in contactwith the substrate, since the mixing ratio of the silicone-modifiedresin or silicone increases as the layer is closer to the surface of therelease sheet, a release sheet having excellent smoothness can beproduced without sacrificing the adhesion between the layers.

In the release sheet for the production of a synthetic leather in eachembodiment of the present invention, the surface resistivity of thesubstrate is preferably not more than 1.0×10¹²Ω. More preferably, thesubstrate contains an organic polymeric conductive agent and/or aninorganic conductive agent, or has, on any one side thereof, a coatingof the organic polymeric conductive agent and/or the inorganicconductive agent, and the content of the conductive agent is in therange of 0.05 to 3.00 g/m² based on the substrate. When the substratehas the above resistivity, the occurrence of static electricity can beprevented at the time of the production of a release sheet and at thetime of the production of a synthetic leather using the release sheet.

According to another aspect of the present invention, there is provideda synthetic leather using the release sheet.

In a preferred embodiment, the synthetic leather of the presentinvention has been produced substantially without the practice ofembossing or/and raising.

According to a further aspect of the present invention, there isprovided a synthetic leather produced by using a release sheet, saidsynthetic leather having a surface arithmetical roughness (Ra) of 0.5 to15 μm and a 85-degree glossiness of 0.5 to 10%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a typical cross-sectional view showing a first embodiment ofthe release sheet for the production of a synthetic leather according tothe present invention;

FIG. 2 is a typical cross-sectional view showing a second embodiment ofthe release sheet for the production of a synthetic leather according tothe present invention;

FIG. 3 is a typical cross-sectional view of a principal partillustrating a synthetic leather production process using a thirdembodiment of the release sheet for the production of a syntheticleather according to the present invention;

FIG. 4 is a typical cross-sectional view showing an example of the thirdembodiment of the release sheet for the production of a syntheticleather according to the present invention;

FIG. 5 is a typical cross-sectional view showing another example of thethird embodiment of the release sheet for the production of a syntheticleather according to the present invention;

FIG. 6 is an electron photomicrograph of the surface of a release sheetfor the production of a synthetic leather prepared in Example 1; and

FIG. 7 is an electron photomicrograph of the surface of a PVC leather 1prepared in Example 1.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in more detailwith reference to the accompanying drawings.

The composition for the formation of a matte layer in a release sheetaccording to the present invention will be first described. Thecomposition for matte layer formation according to the present inventioncomprises a thermosetting resin and a matting agent as indispensablecomponents. The matting agent comprises inorganic or organic porous fineparticles. Inorganic fine particles include fine particles of calciumcarbonate, kaolin, talc, clay, titanium oxide, zinc oxide, silica,alumina, magnesium hydroxide, aluminum hydroxide and the like. Organicfine particles include fine particles of melamine resin, polystyrene,polypropylene, ethylene tetrafluoride resin, silicone resin, starch,acrylic resin and the like. Since, however, the release sheet used inthe production of synthetic leathers is in many cases used under hightemperature conditions, the use of inorganic fine particles is suitablebecause of their excellent heat resistance. Among these inorganic fineparticles, silica, calcium carbonate, and talc are preferred because, asdescribed later, the specific surface area and the particle diametereach can be easily regulated as desired. Silica is particularlypreferred.

These fine particles should be porous. Specifically, in the presentinvention, fine particles having a specific surface area of 1 to 1,000m²/g are used. The pore diameter of the porous fine particles is about50 to 500 angstroms. Assuming that the particle diameter of the fineparticles is identical, the specific surface area depends upon the porediameter and the number of pores. That is, the specific surface areaincreases with reducing the pore diameter and increasing the number ofpores. In the porous fine particles having the above specific surfacearea, that is, a specific pore diameter and a specific number of pores,as the matting agent, light is irregularly reflected from pore portionsformed on the surface of the fine particles. Therefore, a syntheticleather onto which this surface shape has been transferred is jet-blackand is not seen as a faded color. On the other hand, in the case of fineparticles having a diameter of several μm, light scattering is mainlyMie scattering. Since, however, the Mie scattering does not depend uponthe wavelength, the object is seen white. For this reason, in syntheticleathers using a release sheet containing conventional fine particles,the surface is considered to be seen as a faded color. By contrast, inthe release sheet according to the present invention, by virtue of theincorporation of the above porous fine particles in the release sheet,light is also scattered in the pore portion (pore diameter: several tensof angstroms to several hundreds of angstroms) of the fine particles.This scattering is mainly Rayleigh scattering. In the Rayleighscattering, the intensity of scattered light depends upon thewavelength, and the viewer observes both light scattered by Rayleighscattering and light scattered by Mie scattering. It is considered that,for the above reason, synthetic leathers produced using the releasesheet according to the present invention have a matte surface which isjet-black and does not show faded color.

The specific surface area is preferably 10 to 500 m²/g, more preferably100 to 200 m²/g. When the specific surface area is less than 1 m²/g, thenumber of pores present per fine particle is so small that irregularreflection effect cannot be expected. On the other hand, when thespecific surface area of the fine particles exceeds 1,000 m²/g, the porediameter is so small that irregular reflection of light does not occur.Further, when a coating liquid containing porous fine particles havingthe above size is used, the ingredients and the solvent component in thecoating liquid are moderately absorbed into the pores of the fineparticles. Therefore, even when fine particles in a desired amount areincorporated in the coating liquid, the coatability of the coatingliquid is not deteriorated and an even coating can be formed.

The fine particles used in the composition for matte layer formationaccording to the present invention have a mean particle diameter in therange of 1 to 6 μm. The use of the fine particles with particlediameters in the above defined range can realize a synthetic leatherhaving a matte surface which is best to the touch. The particle diameterof the fine particles is preferably 2 to 5 μm, more preferably 2.5 to3.5 μm. When the particle diameter is less than 1 μm, it is difficult toperceive the surface as a matte surface. On the other hand, when theparticle diameter exceeds 6 μm, hitches causative of the drop ofparticles are formed on the surface of the matte layer in the releasesheet. Further, since fine particles are precipitated in the coatingliquid for matte layer formation, the stability of the coating liquid isdeteriorated.

Further, these porous fine particles preferably have been surfacetreated. More preferably, when the thermosetting resin is soluble inwater, the surface treatment is inorganic surface treatment, while, whenthe thermosetting resin is nonaqueous, the surface treatment is organicsurface treatment. The modification of the surface of the fine particleswith an inorganic or organic material can improve the compatibility ofthe fine particles with the thermosetting resin which will be describedlater. In this case, even when the matte layer is formed on thesubstrate, the aggregation of the fine particles can be suppressed. Whena coating liquid is prepared using the surface treated fine particles,the coating liquid has improved fluidity. Therefore, the incorporationof these fine particles in a desired amount in the coating liquid doesnot deteriorate the coatability of the coating liquid.

Organic materials usable herein include polyethylene waxes, paraffinwaxes, and organosilicon compounds. Among them, organosilicon compoundsare particularly preferred.

The matting agent comprising the porous fine particles is preferablycontained in an amount of 5 to 50% by weight in the composition formatte layer formation. When the content of the matting agent in thecomposition is less than 5% by weight, the contemplated matte layercannot be formed. On the other hand, when the content of the mattingagent in the composition exceeds 50% by weight, the coatability of thecomposition onto the substrate is deteriorated and the formation of aneven surface is disadvantageously difficult. The content of the mattingagent in the composition is preferably 7 to 20% by weight, morepreferably 10 to 15% by weight.

Examples of the thermosetting resin constituting the composition formatte layer formation according to the present invention includemelamine resins such as alkyd resins, methylol melamine resins, andmethoxymethylol melamine resins. These resins may be used as a propermixture thereof. In order to suppress the so-called “drop of porous fineparticles” in the release sheet, the use of melamine resin is preferred.

The composition for matte layer formation according to the presentinvention preferably comprises a release agent in addition to the aboveingredients. When the composition contains the release agent, in theproduction of a synthetic leather using the release sheet, the releasesheet can be easily separated from the synthetic leather. Further, theformed synthetic leather has a good surface state. The release agent isnot particularly limited, and examples of release agents usable hereininclude silicones, alkyd resins, alkyd-silicone copolymers, orsilicone-modified amino alkyd resins as disclosed in Japanese PatentLaid-Open No. 28242/1990, and mixtures of the above materials. Thecontent of the release agent is preferably 0 to 60% by weight, morepreferably 30 to 60% by weight. As the content of the release agent isincreased, the synthetic leather can be easily separated from therelease sheet. A release agent content exceeding 60% by weight, however,causes an excessive lowering in frictional resistance of the surface ofthe release sheet which is causative of winding loosing of a releasesheet roll. Further, in the production of a synthetic leather, when asynthetic leather coating material is coated onto the release sheet, thecoating material is repelled from the release sheet due to poorwettability of the release sheet by the coating material.

Next, the release sheet of the present invention produced using theabove composition for matte layer formation and the production processthereof will be described.

FIG. 1 is a typical cross-sectional view showing a first embodiment ofthe release sheet for the production of a synthetic leather according tothe present invention. The construction of a release sheet 10 shown inFIG. 1 is such that a smoothing layer 2 is provided on the upper surfaceof a substrate 1 and a matte layer 3 is provided on the smoothing layer2.

According to this construction, the smoothness of the substrate can beimproved by the smoothing layer. For example, when a material having arelatively rough surface such as paper or a nonwoven fabric is used asthe substrate, the provision of a smoothing layer 2 between thesubstrate 1 and the matte layer 3 is preferred. When the surface of thesubstrate is smoothed, a smooth and even matte layer can be formed. As aresult, in the production of a synthetic leather, it is possible toprevent the pattern present on the surface of the substrate fromappearing as spots on the surface of the synthetic leather. Further,after the production of the synthetic leather, the release sheet can beeasily separated from the synthetic leather without increasing thepeeling resistance.

The smoothing layer can be formed using any composition withoutparticular limitation. An example of a suitable composition forsmoothing layer formation is a composition having the same formulationas the composition for matte layer formation except that the porous fineparticles are absent. This composition can form a smoothing layer whichhas good adhesion to the matte layer and excellent peeling resistance.When the matte layer has a satisfactory thickness, the provision of thesmoothing layer is not always necessary. Since, however, the formationof a thick matte layer results in deteriorated drying properties, thethickness of the matte layer is preferably as thin as possible so far asthe thickness does not adversely affect the formation of fine concavesand convexes 4 on the surface of the matte layer. The formation of athin matte layer, however, sometimes causes surface defects such asspotted dropouts. Therefore, the formation of the smoothing layer ispreferred also from the viewpoint of compensating such defects.

When paper is used as the substrate, the smoothing layer may be a claycoating. In this case, the thickness of the smoothing layer ispreferably about 20 to 40 μm, more preferably 20 to 30 μm. Since theclay coating can smooth the surface of the paper, a matte layer can beuniformly formed on the paper through the clay coating.

The composition for smoothing layer formation may contain a levelingagent. The incorporation of the leveling agent in the composition forsmoothing layer formation can flatten concaves and convexes formed onthe coated face (the surface of the smoothing layer formed on thesubstrate) with the elapse of time. The incorporation of the levelingagent in the composition for smoothing layer formation has such anadditional effect that the occurrence of orange peel, wrinkling,pinholes, foaming, raising, cracking, cratering and the like on thecoating surface can be prevented to smooth the surface.

The leveling agent is not particularly limited so far as the levelingagent used does not deteriorate the adhesion of the smoothing layer tothe matte layer formed on the smoothing layer. Leveling agents usableherein include, for example, silicone resins, such as silicone oils andsilicone-modified resins, and, in addition, polymeric materials calledorganic polymeric leveling agents. For example, when a silicone oil isused as the leveling agent, the silicone oil gathers on the surface ofthe coating to form a kind of a barrier layer. Therefore, theevaporation of the solvent becomes uniform, and the surface tension ofthe coating is lowered, leading to favorable effects. Since, however,the sole use of the silicone oil deteriorates post-adhesion, thecombined use of the organic polymeric leveling agent and the siliconeoil is preferred from the viewpoint of reducing the amount of thesilicone oil added.

The organic polymeric leveling agent is not particularly limited so faras the organic polymeric leveling agent can be dissolved in the resinsolution to lower the surface tension of the resolution and does notlower the post-adhesion. Examples of suitable organic polymeric levelingagents usable herein include polyvinyl butyral and low-molecular weightcellulose. The use of a mixture of these polymeric materials increasesthe viscosity of the coating liquid and suppresses rising of foamsderived from dynamic viscosity and thus results in the formation of asmooth coating surface. The “post-adhesion” as used herein refers to theadhesion between the smoothing layer and the matte layer. When thisadhesion is low, in the production of a synthetic leather, upon theseparation of the release sheet from the synthetic leather, the mattelayer, together with the synthetic leather, is disadvantageouslyseparated from the smoothing layer.

For example, internally curable silicone resins or fluorocopolymerresins may also be used as the leveling agents, although these resinsare inferior to the above polymeric leveling agents in thepost-adhesion.

Internally curable silicone resins include silicone acrylates, andspecific examples thereof include acrylsilanes and methacrylsilanes,acrylsilicones and methacrylsilicones, and phenylsilicone acrylate andm-phenylsilicone acrylate. More specific examples thereof includeacrylsilanes such as acryloxypropylmethyldimethoxysilane andacryloxypropyltrimethoxysilane, and methacrylsilanes such asmethacryloxypropylmethyldimethoxysilane, andmethacryloxypropyltrimethoxysilane.

Further, the so-called “surfactant” or the like may be used as theorganic polymeric leveling agent. Since, however, this function to lowerthe surface tension, solvents used are limited and, for example, aqueouscoating, such as alcoholic or emulsion coating, is necessary.

When organic solvent systems are used, the above-described polymericmaterials, silicone-modified copolymer resins, fluorocopolymer resinsand the like may be used as the organic polymeric leveling agent.Specific examples thereof include Chaline Series manufactured by NissinChemical Industry Co., Ltd. Further, for example, Talen, Flowlen, andPolyflow, which are organic copolymers such as low-molecular weightcellulose, manufactured by Kyoeisha Chemical Co., Ltd. are alsopreferred.

Two or more organic polymeric leveling agents can also be used incombination. For example, the addition of an internally curable siliconein addition to a low-molecular weight cellulose can also provide goodresults.

The amount of the organic polymeric leveling agent added is preferablyabout 0.01 to 3% by weight based on the composition for smoothing layerformation. If the amount of the organic polymeric leveling agent addedis less than 0.01% by weight, then the leveling effect cannot beattained, while if it exceeds 3% by weight, the post-adhesion isdisadvantageously lowered.

FIG. 2 shows a second embodiment of the release sheet for the productionof a synthetic leather according to the present invention. As shown inFIG. 2, the matte layer 3 has a multilayer structure of two or morelayers, i.e., releasable resin layers (3 a and 3 b), and, among thelayers constituting the multilayered matte layer, each of all thereleasable resin layers 3 a except for at least the layer 3 b in contactwith the surface of the substrate contains a release agent comprising asilicone-modified resin or a silicone-containing resin composition. Inthis case, as the layer is closer to the surface of the matte layer, thecontent of the release agent is increased.

When the formation of a matte layer having high smoothness by coatingthe resin with a silicone resin or the like added thereto and drying thecoating is contemplated, the resin should be coated to a largethickness. Coating of the resin to a large thickness, however,deteriorates the drying properties of the coating. Acceleration of thedrying by strong heating or the like for solving this problemdeteriorates the smoothness of the matte layer. A solution to thisproblem is to form a multilayered matte layer. When the resin for mattelayer formation contains a silicone-modified resin or a silicone,however, mere stacking of coatings formed using coating liquids havingthe same composition poses a problem that the receptivity or adhesion tolater stacked layers for constituting the matte layer is deteriorated.

In the release sheet according to the present invention, as describedabove, the formation of a matte layer having a multilayer structure ofreleasable resin layers is advantageous in that, even when the formationof a thick matte layer is contemplated due to unsatisfactory smoothnessof the substrate, the thickness of each of the layers constituting thematte layer can be made small and, in addition, the lower release layercan improve the smoothness, whereby a smooth matte layer can beefficiently formed without sacrificing the drying properties. Further,among the layers constituting the multilayered matte layer, all thereleasable resin layers except for at least the innermost layer, thatis, the outer releasable resin layers, contain a silicone-modified resinor silicone, and, in addition, as the releasable resin layer is closerto the outer surface of the matte layer, the content of thesilicone-modified resin or silicone in the releasable resin layer ishigher. Therefore, the adhesion between the releasable resin layers isnot deteriorated.

What is required of the innermost layer constituting the multilayeredmatte layer is only to function as a smoothness improving layer, and thereleasability is not required of the innermost layer. Therefore, theaddition of the silicone-modified resin or silicone as the release agentto the innermost releasable resin layer is not necessary. That is, inthe innermost releasable resin layer, the mixing ratio of thesilicone-modified resin or silicone may be 0 (zero). Since, however,good leveling is necessary, the silicone-modified resin or silicone maybe used as a leveling agent in a limited minor amount. When thesilicone-modified resin or silicone is used as the leveling agent, thesilicone-modified resin or silicone may be used in combination with theabove leveling agent, or alternatively other leveling agents may be usedinstead of the silicone-modified resin or silicone.

The third embodiment of the release sheet for the production of asynthetic leather according to the present invention comprises: a mattelayer having fine concaves and convexes on its surface; and a substratefor supporting the matte layer, said matte layer comprising a releasableresin layer, a releasable transparent resin being provided so as to stayon the bottom of the concaves in the concave-convex portion. The use ofthe release sheet having a matte layer in which a transparent resinstays on the bottom of the concaves in the concave-convex portion canrealize the production of a synthetic leather which is finer to thetouch, that is, has the so-called “peach skin-like” feel. Further, whenthe transparent resin is used, synthetic leathers with different colorsor with a light color can be continuously produced without the influenceof the color of the previously produced synthetic leather and therelease sheet can be repeatedly used with safety.

FIG. 3 is a typical cross-sectional view of a principal partillustrating the step of allowing a part of a coated transparentsynthetic resin layer to stay on the bottom of the concaves in the fineconcave-convex portion on the surface of the releasable resin layer inthe release sheet according to the present invention.

After a matte layer 3 is formed on a substrate 1, a transparentsynthetic resin liquid is coated onto the matte layer 3 to form acoating which is then heat dried to form a transparent synthetic resinlayer 5. The transparent synthetic resin layer 5 is then separated fromthe release sheet 10. Thus, a broken transparent synthetic resin 5′stays on the bottom of the concaves in the fine concaves and convexes 4of the matte layer 3.

More specifically, a transparent synthetic resin liquid is coated ontothe surface of the matte layer 3 in the release sheet 10. In this case,the synthetic resin liquid also enters the concaves in the fine concavesand convexes. The coating is brought into a film, for example, by heatdrying to form a transparent synthetic resin layer 5. When thetransparent synthetic resin layer 5 is then separated from the releasesheet 10, the transparent synthetic resin layer 5, which has entered theconcaves in the fine concaves and convexes, is broken partway becausethe peeling resistance at the time of separation is larger than thebreaking strength. As a result, a transparent synthetic resin 5′ remainsunremoved on the bottom of the concaves (see FIG. 4). The broken face ofthe transparent synthetic resin 5′ remaining unremoved is in anirregular and fine concave-convex form. Therefore, the whole surface ofthe matte layer 2 is in the form of fine concaves and convexes withdifferent finesses which are suitable for imparting a peach skin-likefeel to the surface of the synthetic leather. Accordingly, when asynthetic leather is produced using this release sheet, a peachskin-like feel can be imparted to the surface of the synthetic leather.

The resin used is not particularly limited. However, a part of theresin, which has entered the concaves, should be broken with properbreaking strength. To this end, for example, a resin composition havingthe same formulation as the resin composition for the formation of askin layer in a synthetic leather except for the absence of the colorantcan be suitably used. Specific examples of resin compositions usableherein include a polyurethane composition in a paste form for apolyurethane leather (hereinafter referred to simply as “PU leather”),in which additives other than the colorant may be contained and thesolid content is about 20 to 50% by weight, and a polyvinyl chloridecomposition for a PVC leather, in which a PVC sol is generally used and,likewise, additives other than the colorant, for example, a plasticizerand a stabilizer, may be contained. The above synthetic resin may becoated by a conventional coating method such as knife coating, rollcoating, or gravure coating. As shown in FIG. 5, the smoothing layer 2as described above may also be provided between the matte layer and thesubstrate.

Papers such as kraft papers, wood free papers, and cast coated papersmay be used as the substrate for supporting the smoothing layer and thematte layer. Other materials usable as the substrate include: films ofplastics, for example, polyesters such as polyethylene terephthalate andpolyethylene naphthalate, polyamides such as various nylons, andpolypropylene; synthetic papers; metal foils; woven fabrics; andnonwoven fabrics. These materials may be used solely or as a properlaminate of two or more of them.

The substrate preferably has a surface resistivity (Ω) of not more than1.0×10¹². In particular, preferably, the substrate contains an organicpolymeric conductive agent and/or an inorganic conductive agent, or has,on any one side thereof, a coating of the organic polymeric conductiveagent and/or the inorganic conductive agent, and the content of theconductive agent is in the range of 0.05 to 3.00 g/m² based on thesubstrate.

When the resistivity of the substrate is in the above defined range,antistatic effect can be attained. That is, at the time of the formationof the matte layer and at the time of the production of a syntheticleather using the release sheet, cracking of the surface of the mattelayer or of the synthetic leather by the occurrence of staticelectricity can be prevented.

A possible formulation of main materials for constituting the substrateis as follows. Regarding a pulp formulation, bleached kraft pulp of abroad-leaved tree (L-BKP) and bleached kraft pulp of a needle-leavedtree (N-BKP) are used as main pulp fibers, and waste stuff or wastepaper pulp is properly mixed thereinto. Further, internal sizing agents,cationized starches, and antifoaming agents, such as fatty esters andspecial paraffins, and the like may be used as additives. In a substratesize press process, a size press liquid containing a corn starch, asurface sizing agent, a conductive agent and the like is coated onto abase paper. In this size press process, the size press liquid is coatedon both sides of the substrate and is also impregnated into thesubstrate.

Conductive agents usable herein are organic polymeric conductive agentsand/or inorganic conductive agents. Organic polymeric conductive agentsinclude: nonionic polymers such as polyvinyl alcohol, polyacrylamide,and polyethylene glycol; anionic polar group-containing polymers such assulfonated styrene resin; and cationic polymers, for example, quaternaryammonium salts such as quaternary ammonium chloride. Inorganicconductive agents include calcium oxide, sodium aluminate, zinc oxide,tin oxide, calcium chloride, lithium chloride, potassium chloride,magnesium chloride, sodium chloride, and carbon black.

The content of the conductive agent or the coverage of the conductiveagent on the surface of the substrate may be in the range of 0.05 to 3.0g/m², preferably in the range of 0.2 to 2.0 g/m². When the amount of theconductive agent is less than 0.05 g/m², the surface resistivity of thesubstrate is likely to exceed 1.0×10¹²Ω and, consequently, theantistatic effect is unsatisfactory. For this reason, at the time of theformation of the matte layer or at the time of the production of asynthetic leather using this type of release sheet, cracking occurs inthe matte layer or the synthetic leather due to the generation of staticelectricity. On the other hand, when the amount of the conductive agentexceeds 3.0 g/m², a further improvement in the antistatic effect cannotbe expected and, further, in this case, the material cost isdisadvantageously increased.

On the other hand, when a plastic film or a metal foil is used as thesubstrate, the provision of the smoothing layer is unnecessary becausethe surface of the plastic film or metal foil is generally smooth. Insome cases, however, the adhesion to the matte layer is unsatisfactory.In this case, the surface of the substrate may be subjected toeasy-adhesion treatment such as corona discharge treatment or ozonetreatment, or alternatively a primer coating or the like may be appliedto the surface of the substrate.

A smoothing layer and a matte layer are formed on the substrate. In theformation of the smoothing layer, the composition for smoothing layerformation is provided as a coating liquid, and the coating liquid iscoated, for example, by a coating method such as bar coating, air doctorcoating, blade coating, squeeze coating, air knife coating, rollcoating, gravure coating, transfer coating, Komma coating, smoothingcoating, microgravure coating, reverse roll coating, multiroll coating,dip coating, rod coating, kiss coating, gate roll coating, drop curtaincoating, slide coating, fountain coating, or slit die coating. After thecoating liquid is coated, the coating is dried and solidified to form asmoothing layer. Next, the composition for matte layer formation isprovided as a coating liquid and may be coated in the same manner asdescribed above to form a matte layer.

In the release sheet thus produced, the thickness of the smoothing layeris preferably 0.5 to 10 g/m² in terms of coverage after drying of thecoating. If the thickness of the smoothing layer is less than 0.5 g/m²,then the contemplated effect of the smoothing layer cannot be expected.On the other hand, a thickness of more than 10 g/m² causes a lowering indrying speed and processing speed and is also disadvantageous from theviewpoint of cost.

The thickness of the matte layer is preferably in the range of 1.0 to 20g/m² in terms of coverage after drying of the coating. If the thicknessof the matte layer is less than 1.0 g/m², then the formation of an evencoating is difficult. Coating to a larger thickness is preferred fromthe viewpoint of providing a satisfactorily matte surface or from theviewpoint of releasability. A thickness exceeding 20 g/m², however,causes a lowering in drying speed and processing speed and is alsodisadvantageous from the viewpoint of cost.

In the release sheet thus obtained, a fine concave-convex portion 4 isformed on the surface of the matte layer, and the arithmetical meanroughness (Ra) of the matte surface is 0.5 to 15 μm. More preferably,the mean spacing of profile irregularities (concaves and convexes) (Sm)in the concave-convex portion on the surface of the matte layer is 0.5to 10 μm.

In the release sheet in which a transparent resin is provided so as tostay in the concaves, preferably, the concave-convex portion has anarithmetical mean roughness (Ra) of 0.5 to 15 μm, the mean spacing ofprofile irregularities (concaves and convexes) (Sm) in theconcave-convex portion is 0.5 to 10 μm, and the mean inclination (θa) ofthe concaves and convexes is 45 degrees≦θa<90 degrees. The arithmeticalmean roughness (Ra) of the fine concaves and convexes and the meanspacing of profile irregularities (concaves and convexes) (Sm) arevalues measured based on JIS B 0601-1994 “Surface roughness —Definitionsand designation” under the following measuring conditions.

Measuring Conditions

Tip radius of stylus: load 5 μm: cut-off value 4 mN: standard valuedescribed in Table 1 is selected.

Reference length: standard value described in Table 2 is selected.

Measuring instrument: surface roughness measuring device Suftest-201,manufactured by MITUTOYO CORPORATION

TABLE 1 Cut-off value λc, Evaluation length Ra range, μm mm Ln, mm 0.006< Ra ≦ 0.02 0.08 0.4 0.02 < Ra ≦ 0.1 0.25 1.25 0.1 < Ra ≦ 2.0 0.8 4.02.0 < Ra ≦ 10.0 2.5 12.5 10.0 < Ra ≦ 80.0 8.0 40.0

TABLE 2 Reference length Evaluation length Sm range, μm L, mm Ln, mm0.013 < Sm ≦ 0.04 0.08 0.4 0.04 < Sm ≦ 0.13 0.25 1.25 0.13 < Sm ≦ 0.40.8 4.0 0.4 < Sm ≦ 1.3 2.5 12.5 1.3 < Sm ≦ 4.0 8.0 40.0

A synthetic leather can be produced using the above release sheet byconventional paste coating method (vinyl chloride leather method;hereinafter referred to as “PVC leather method”) or dry method(polyurethane leather method; hereinafter referred to as “PU leathermethod”).

Specifically, a synthetic leather with fine concaves and convexes beingformed on the surface thereof can be produced by coating a resincomposition for a skin layer in a synthetic leather onto the surface ofa matte layer in the release sheet, drying the coating by heating toform a film as the skin layer, then laminating a backing fabric onto theskin layer with the aid of an adhesive, drying and aging the assembly,and then separating the release sheet.

For example, in the formation of the PVC leather, a PVC paste, whereinpolyvinyl chloride is used as a main component and a plasticizer, afoaming agent, a stabilizer, a colorant and the like have been properlyadded to polyvinyl chloride, may be used as the resin composition for askin layer in the synthetic leather. In the formation of the PU leather,a composition having a solid content of about 20 to 50% by weightprepared by optionally adding a colorant and other additives to apolyurethane solution may be used. The above composition for skin layerformation may be coated by conventional coating means such as knifecoating, roll coating, reverse roll coating, or gravure coating.

The synthetic leather produced by the above method is a matte syntheticleather which has a matte surface with a high level of jet-blacknesswithout the practice of embossing, raising or the like. Further, sincethe surface shape of the release sheet is transferred onto the surfaceof the synthetic leather, the surface of the synthetic leather has anarithmetical roughness (Ra) of 0.5 to 15 μm and a glossiness in therange of 0.5 to 10% as measured in 85-degree incidence/85-degreereflection.

Further, the synthetic leather produced using the release sheet with atransparent resin staying in the concave portion of the matte layer hason its surface a releasable transparent resin layer. Therefore, thesurface of the synthetic leather has a peach skin-like feel and, at thesame time, is less likely to be soiled and, even when soiled, can beeasily cleaned because the soil can be easily removed.

The following examples further illustrate the present invention but arenot intended to limit it. It should be noted that any technical idea,which has constitution and function and effect substantially identicalto that described in claims of the present invention, are embracedwithin the technical scope of the present invention.

EXAMPLES Examples 1 to 3

A cast coated paper having a basis weight of 155 g/m² manufactured byOji Paper Co., Ltd. was provided as a substrate. A coating liquid forsmoothing layer formation having the following composition was rollcoated onto the cast coated face at a coverage of 5 g/m² on a dry basis,and the coating was dried by heating at 160° C. for one min or longer toform a smoothing layer.

Composition of coating liquid for smoothing layer formation Melamineresin (Melan 28, manufactured 220 pts. wt. by Hitachi Chemical Co.,Ltd.) Alkyd resin (Phthalkyd 133-60, 100 pts. wt. manufactured byHitachi Chemical Co., Ltd.) Acid catalyst (p-toluenesulfonic acid)  8.4pts. wt. Solvent (toluene/n-butyl alcohol: 980 pts. wt. weight ratio =1/1)

Next, coating liquids for matte layer formation having the followingcompositions containing various types of silica shown in Table 3 wereroll coated onto the smoothing layer at a coverage of 10 g/m² on a drybasis, and the coatings were dried by heating at 180° C. for one min orlonger to form matte layers. Thus, release sheets of Examples 1 to 3were prepared.

Coating liquid for matte layer formation Methylolated melamine resin 50pts. wt. Silicone-modified alkyd resin 50 pts. wt. Acid catalyst(p-toluenesulfonic 4.2 pts. wt. acid) Porous fine particles (silica: 10pts. wt. see Table 2) Solvent (toluene/n-butyl alcohol: 500 pts. wt.weight ratio = 1/1)

The coating liquids for matte layer formation, when coated on thesmoothing layer, could be evenly coated without cissing, and, uponcuring by heating, each of the coatings could form a smoothing layerhaving good adhesion to the matte layer. FIG. 6 shows an electronphotomicrograph of the surface of the release sheet produced in Example1.

For the release sheets of Examples 1 to 3 thus prepared, thearithmetical mean roughness (Ra) of the surface of the matte layer isshown in Table 3.

The following two synthetic leathers, a PVC leather and a PU leather,were prepared using the release sheets of Examples 1 to 3 thus obtained.

Preparation of Matte PVC Leather

A PVC composition (paste), for the formation of a skin layer in asynthetic leather, prepared by mixing 100 parts by weight of a PVC resin(molecular weight 1,000), 60 parts by weight of a plasticizer DOP, 5parts by weight of a foaming agent, 2.5 parts by weight of a stabilizer,and 15 parts by weight of a colorant (SEIKASEVEN NET-5794 Black,manufactured by Dainichiseika Color & Chemicals Manufacturing Co., Ltd.)together was knife coated onto the surface of the matte layer in therelease sheet of Example 1 at a coverage of 150 g/m² on a dry basis. Thecoating was dried by heating at 190 to 200° C. for 2 min or longer.Thereafter, a backing fabric was applied onto the dried coating with theaid of an adhesive, and the laminate was dried and aged. The releasesheet was then separated and removed to prepare a PVC leather 1.

The PVC leather 1 thus obtained could be easily separated from therelease sheet without significant peeling resistance and had a mattesurface with a high level of jet-blackness. The glossiness of the PVCleather thus obtained was measured under conditions of 85-degreeincidence/85-degree reflection. The results of the measurement ofsurface glossiness of the PVC leather are shown in Table 3. FIG. 7 showsan electron photomicrograph of the surface of the PVC leather 1 preparedin Example 1.

Preparation of Matte PU Leather

A PU composition (paste), for the formation of a skin layer in asynthetic leather, prepared by mixing 100 parts by weight ofpolyurethane (Resamine NE-8811, manufactured by Dainichiseika Color &Chemicals Manufacturing Co., Ltd.), 15 parts by weight of a colorant(SEIKASEVEN NET-5794 Black, manufactured by Dainichiseika Color &Chemicals Manufacturing Co., Ltd.), 25 parts by weight of toluene, and25 parts by weight of isopropyl alcohol together was knife coated ontothe surface of the matte layer in the release sheet of Example 1 at acoverage of 150 g/m² on a dry basis. The coating was dried by heating at100 to 120° C. for 2 min or longer. Thereafter, a backing fabric wasapplied onto the dried coating with the aid of an adhesive, and thelaminate was dried and aged. The release sheet was then separated andremoved to prepare a PU leather 1.

The PU leather 1 thus obtained could be easily separated from therelease sheet without significant peeling resistance and had a mattesurface with a high level of jet-blackness. Even after the repetition ofthe preparation of the PU leather 1 three times or more, the leather hadthe same matte surface as in the first preparation of the syntheticleather.

Comparative Examples 1 and 2

Release sheets were prepared in the same manner as in Example 1, exceptthat fine particles shown in Table 3 were used instead of the porousfine particles used in the coating liquid for matte layer formation inExample 1. Synthetic leathers were prepared in the same manner as inExample 1, except that the release sheets prepared just above were used.The arithmetical mean roughness (Ra) of the release sheets thus obtainedand the glossiness of the PVC leathers produced using the release sheetswere measured, and the results are shown in Table 3.

TABLE 3 Release Fine particles (silica) sheet Particle Specific SurfacePVC leather diameter, surface Surface roughness Glossiness, μm area,m²/g treatment Ra, μm % Ex. 1 2.5 150 Organic 2.0 1.2 Ex. 2 1.0 200Organic 1.0 1.1 Ex. 3 10.0 60 Organic 10.2 1.6 Comp. 2.5 1500 Organic2.1 17.0 Ex. 1 Comp. 2.5 0.1 Inorganic 1.7 20.0 Ex. 2

Example 4 Preparation of PVC Leather Having Combination of Matte Tonewith Peach Skin Tone

A release sheet 4 was prepared in quite the same manner as in Example 1,except that a mixture of 10 parts by weight of silica, which had beensubjected to organic surface treatment and had a mean particle diameterof 5.2 μm (specific surface area: 340 to 350 m²/g) (SYLYSIA 456,manufactured by Fuji Silysia Chemical Ltd.), with 10 parts by weight ofsilica which had been subjected to organic surface treatment and had amean particle diameter of 2.5 μm (specific surface area: 340 to 350m²/g) (SYLYSIA 436, manufactured by Fuji Silysia Chemical Ltd.) was usedas the porous fine particles. Skin layers for a synthetic leather wereformed on the surface of the matte layer in the release sheet 4 asfollows. At the outset, a PVC composition (paste) prepared by mixing 100parts by weight of PVC (molecular weight 1,000), 60 parts by weight of aplasticizer (DOP), and 1 (one) part by weight of a water-dispersedsilicone release agent (amino-modified silicone) together was gravurecoated at a coverage of 2 g/m² on a dry basis, and the coating wasdried. Next, a PVC composition (paste), for skin layer formation in asynthetic leather, prepared by mixing 100 parts by weight of a PVC resin(molecular weight 1,000), 60 parts by weight of a plasticizer DOP, 5parts by weight of a foaming agent, 2.5 parts by weight of a stabilizer,and 15 parts by weight of a colorant (SEIKASEVEN NET-5794 Black,manufactured by Dainichiseika Color & Chemicals Manufacturing Co., Ltd.)together was knife coated thereon at a coverage of 150 g/m² on a drybasis, and the coating was then dried by heating at 190 to 200° C. for 2min or longer. Thereafter, a backing fabric was applied onto the driedcoating with the aid of an adhesive, and the laminate was dried andaged. The release sheet was then separated and removed to prepare a PVCleather 4.

The PVC leather 4 thus obtained had a releasable thin transparent PVCresin layer on its surface, and the surface thereof was a fine touchsurface having a combination of a matte tone with a peach skin tone.After the separation of the release sheet, the PVC transparent resinremained unremoved on the bottom of the concaves in the fineconcave-convex portion on the surface of the release sheet, and thecolored PVC (PVC leather side) resin was not transferred onto and wasabsent on the release sheet side.

The preparation of PVC leather with different colors was repeated fivetimes using the release sheet in Example 4 in the same manner as inExample 4. As a result, the release sheet could be easily separated fromthe synthetic leather without significant peeling resistance. Further,since the release sheet could be continuously used without the transferof the colored PVC resin in the leather skin layer onto the releasesheet, PVC leathers having an excellent matte surface could beefficiently produced.

Example 5 Preparation of PU Leather Having Combination of Matte Tonewith Peach Skin Tone

Skin layers for a synthetic leather were formed on the surface of thematte layer in the same release sheet as prepared in Example 4 asfollows. At the outset, a coating liquid prepared by mixing 100 parts byweight of a polyurethane composition (Resamine NE-8811, manufactured byDainichiseika Color & Chemicals Manufacturing Co., Ltd.), 0.5 part byweight of a silicone release agent (amino-modified silicone), 0.5 partby weight of epoxy-modified silicone, and 25 parts by weight of tolueneand 25 parts by weight of isopropyl alcohol (hereinafter referred to as“IPA”) as solvents together was gravure coated on the surface of thematte layer at a coverage of 1.5 g/m² on a dry basis, and the coatingswere then dried. Next, a PU composition (black colored paste), for theformation of a skin layer in a synthetic leather, prepared by mixing 100parts by weight of polyurethane (Resamine NE-8811, manufactured byDainichiseika Color & Chemicals Manufacturing Co., Ltd.), 15 parts byweight of a colorant (SEIKASEVEN NET-5794 Black, manufactured byDainichiseika Color & Chemicals Manufacturing Co., Ltd.), 25 parts byweight of toluene, and 25 parts by weight of IPA together was knifecoated thereon at a coverage of 150 g/m² on a dry basis, and the coatingwas dried by heating at 100 to 120° C. for 2 min or longer. Thereafter,a backing fabric was applied onto the dried coating with the aid of anadhesive, and the laminate was dried and aged. The release sheet wasthen separated and removed to prepare a PU leather 5.

The PU leather 5 thus obtained had a releasable thin transparent PUresin layer on its surface, and, as with the synthetic leather preparedin Example 4, the PU leather 5 had a surface with a combination of amatte tone having a high level of jet-blackness with a peach skin tone.After the separation of the release sheet, the PU transparent resinremained unremoved on the bottom of the concaves in the fineconcave-convex portion on the surface of the release sheet, and thecolored PU (PU leather side) resin was not transferred onto and wasabsent on the release sheet side.

The preparation of PU leather with different colors was repeated fivetimes using the release sheet in Example 5 in the same manner as inExample 5. As a result, the release sheet could be easily separated fromthe synthetic leather without significant peeling resistance. Further,since the release sheet could be continuously used without the transferof the colored PU resin in the leather skin layer onto the releasesheet, PU leathers having an excellent matte surface could beefficiently produced.

Example 6

A release sheet 6 was prepared in quite the same manner as in Example 1,except that 40 parts by weight of silica, which had been subjected toorganic surface treatment and had a mean particle diameter of 5.2 μm(specific surface area: 340 to 350 m²/g) (SYLYSIA 456, manufactured byFuji Silysia Chemical Ltd.), was used as the porous fine particles.

Fine concaves and convexes formed on the surface of the matte layer inthe release sheet 6 had an arithmetical mean roughness (Ra) of 0.54 μm,a mean profile irregularity spacing (Sm) of 9 μm, and a mean inclination(θa) of 47 degrees and were good as fine concaves and convexes forimparting peach skin-like appearance and touch to the surface of thesynthetic leather.

A PU leather with a skin layer having a two-layer structure of areleasable thin transparent resin layer provided on the surface side anda colored resin layer provided on the inner layer side was prepared asfollows. At the outset, a coating liquid prepared by mixing 100 parts byweight of a polyurethane composition (Resamine NE-8811, manufactured byDainichiseika Color & Chemicals Manufacturing Co., Ltd.), 0.5 part byweight of a silicone release agent (amino-modified silicone), 0.5 partby weight of epoxy-modified silicone, and 25 parts by weight of tolueneand 25 parts by weight of IPA as solvents together was gravure coated onthe surface of the matte layer in the release sheet 6 at a coverage of2.0 g/m² on a dry basis, and the coatings were then dried. Next, a PUcomposition (red colored paste), for the formation of a skin layer in asynthetic leather, prepared by mixing 100 parts by weight ofpolyurethane (Resamine NE-8811, manufactured by Dainichiseika Color &Chemicals Manufacturing Co., Ltd.), 15 parts by weight of a colorant(SEIKASEVEN NET-5194 Red, manufactured by Dainichiseika Color &Chemicals Manufacturing Co., Ltd.), 25 parts by weight of toluene, and25 parts by weight of IPA together was knife coated thereon at acoverage of 150 g/m² on a dry basis, and the coating was dried byheating at 100 to 120° C. for 2 min or longer. Thereafter, a backingfabric was applied onto the dried coating with the aid of an adhesive,and the laminate was dried and aged. The release sheet was thenseparated and removed to prepare a PU leather 6.

In the PU leather 6 thus obtained, the skin layer had such aconstruction that a releasable thin transparent PU resin layer wasprovided on the upper surface of a colored PU resin layer. By virtue ofthis construction, the PU leather 6 had unique soft color impression andhad good peach skin-like appearance and feel. After the separation ofthe release sheet, the PU transparent resin remained unremoved on thebottom of the concaves in the fine concave-convex portion on the surfaceof the release sheet, and the colored PU (PU leather side) resin was nottransferred onto and was absent on the release sheet side.

The preparation of PU leather with different colors was repeated fivetimes using the release sheet in Example 5 in the same manner as inExample 5. As a result, the release sheet could be easily separated fromthe synthetic leather without significant peeling resistance. Further,since the release sheet could be continuously used without the transferof the colored PU resin in the leather skin layer onto the releasesheet, PU leathers having an excellent matte surface could beefficiently produced.

1. A process for producing a synthetic leather comprising the steps of:coating a resin composition for a skin layer of the synthetic leatheronto a surface of a matte layer of a release sheet, drying the coatingby heating to form a film as the skin layer, then laminating a backingfabric onto the skin layer with the aid of an adhesive to form anassembly, drying and aging the assembly, and then separating the releasesheet from the assembly to form the synthetic leather, wherein therelease sheet comprises: a matte layer formed by coating a compositionfor matte layer formation comprising a thermosetting resin, a releaseagent, and a matting agent as indispensable components, said mattingagent comprising at least one of organic and inorganic porous fineparticles, said porous fine particles having a mean particle diameter of0.5 to 20 μm and a specific surface area of 1 to 1000 m²/g; and asubstrate for supporting the matte layer, wherein said matte layer is areleasable resin layer having a multilayer structure of at least twolayers; all the releasable resin layers constituting the multilayeredmatte layer, except for at least a layer in contact with the substrate,contain a release agent comprising a silicone-modified resin or asilicone-containing resin composition; a content of the release agent inthe releasable resin layer is greater in releasable resin layers thatare closer to a surface of the matte layer; and all the releasable resinlayers constituting the multilayered matte layer, except for at least alayer in contact with the substrate, further comprise a leveling agent.2. The process according to claim 1, wherein the skin as the outermostlayer in the synthetic leather is a transparent resin layer.
 3. Theprocess according to claim 2, wherein the transparent resin layer isreleasable.
 4. The process according to claim 1, which has been producedsubstantially without embossing or/and raising.
 5. The process accordingto claim 1, the synthetic leather having a surface arithmeticalroughness (Ra) of 0.5 to 15 μm and a 85-degree glossiness of 0.5 to 10%.